SAN JOSE, the United States, Aug. 26 (Xinhua) -- NASA's Mars rover Opportunity is heading back out to the Red Planet's surrounding plains nearly a year after descending into a large Martian crater to examine exposed ancient rock layers.

    "We've done everything we entered Victoria Crater to do and more," said Bruce Banerdt, of NASA's Jet Propulsion Laboratory in California. Banerdt is project scientist for Opportunity and its rover twin, Spirit.

    Having completed its job in the crater, Opportunity is now preparing to inspect loose cobbles on the plains. Some of these rocks, approximately fist-size and larger, were thrown long distances when objects hitting Mars blasted craters deeper than Victoria into Mars. Opportunity has driven past scores of cobbles but examined only a few.

    Engineers are programming Opportunity to climb out of the crater at the same place it entered. The big crater stretches approximately a half mile (0.8 km) in diameter and is deeper than any other seen by Opportunity.

    Opportunity entered Victoria Crater on Sept. 11, 2007, after a year of scouting from the rim. Once a drivable inner slope was identified, the rover used contact instruments on its robotic arm to inspect the composition and textures of accessible layers.

    The rover then drove close to the base of a cliff called "Cape Verde," part of the crater rim, to capture detailed images of a stack of layers. The information Opportunity has returned about the layers in Victoria suggest the sediments were deposited by wind and then altered by groundwater.